High intensity discharge lamps with a high UV or "blue" output are often used for medical purposes. One example is a short arc mercury lamp that produces a rich spectrum in the ultraviolet (UV) near 365 nanometers. Other examples of UV discharge light sources are suntan lamps which are basically fluorescent lamps with near UV emitting phosphors to produce UV A or UV B. Mercury lamps without phosphor and quartz envelopes are frequently used to generate high energy UV for disinfectant purposes. High pressure xenon arc lamps, for example Cermax lamps, are used for medical illumination.
Lamps are also used to cure polymers used in dental reconstructive procedures where the UV or blue light is needed to crosslink the molecules to form a solid material. The UV curing application is used with the polymeric lamp filler materials to repair dental caries. Occasionally, these chemical systems require concentrated light in a specific spectral band and other light is wasted. Often it is important to shield the patient from unnecessary light, since the fluxes can be high. Such light delivery systems can be inefficient, since many watts of input electric power are used to produce only a few watts of useable blue light.
Methods of spectral tailoring the blue light from a source have included phosphor emission which is limited to a spatially extended source. Other methods include filtering the broadband emission, such as from a more compact halogen incandescent lamp to achieve the desired spectral pass band. Another method is to use a laser which can provide light in the desired spectral region such as an argon ion laser with atomic emission lines at 457 and 458 nanometers. Blue lasers are expensive to operate and usually require a skilled operator. The laser systems pose the additional problem of shielding the patient from coherent light and must follow strict exposure guidelines. Still, another alternative is a blue emitting solid state laser or LED. Currently, blue laser or LED devices have low power or are unreliable, having operating lifetimes of about 100 hours.
Often it is necessary to have light within a specific spectral band and any out-of-band light must be rejected or converted into heat. Electrodeless high intensity discharge (EHID) lamps can offer an advantage in this area since EHID lamp fills can be tailored to emit in the pass bands of interest with minimal radiation outside the band (waste). Consequently, there is minimal conversion of excess light into heat. There is then a general need for an intense, efficient blue light.